Ultralow-iridium content NiIr alloy derivative nanochain arrays as bifunctional electrocatalysts for overall water splitting

Abstract

The development of low-cost and high-durability bifunctional electrocatalysts is of considerable importance for overall water splitting (OWS). This work reports the controlled synthesis of nickel–iridium alloy derivative nanochain array electrodes (NiIr_x NCs) with fully exposed active sites that facilitated mass transfer for efficient OWS. The nanochains have a self-supported three-dimensional core–shell structure, composed of a metallic NiIr_x core and a thin (5–10 nm) amorphous (hydr)oxide film as the shell (e.g., IrO₂/NiIr_x and Ni(OH)₂/NiIr_x). Interestingly, NiIr_x NCs have bifunctional properties. Particularly, the oxygen evolution reaction (OER) current density (electrode geometrical area) of NiIr₁ NCs is four times higher than that of IrO₂ at 1.6 V vs. RHE. Meanwhile, its hydrogen evolution reaction (HER) overpotential at 10 mA cm⁻² (η₁₀ = 63 mV) is comparable to that of 10 wt% Pt/C. These performances may originate from the interfacial effect between the surface (hydr)oxide shell and metallic NiIr_x core, which facilitates the charge transfer, along with the synergistic effect between Ni²⁺ and Ir⁴⁺ in the (hydr)oxide shell. Furthermore, NiIr₁ NCs exhibits excellent OER durability (100 h @ 200 mA cm⁻²) and OWS durability (100 h @ 500 mA cm⁻²) with the nanochain array structure well preserved. This work provides a promising route for developing effective bifunctional electrocatalysts for OWS applications.